Physical properties and antioxidant capacity of starch–sodium caseinate films containing lipids

Biodegradable films based on starch, sodium caseinate, glycerol and lipids (oleic acid and/or α-tocopherol) were obtained and evaluated in terms of microstructure, mechanical behaviour, barrier and optical properties and antioxidant capacity. The effect of film storage time on these properties was also analysed. The lipid incorporation provoked phase separation due to the different interaction between each polymer and lipids, although structural rearrangement of components during storage could be deduced from the change in mechanical behaviour. After storage, all films showed similar mechanical properties, but lipid containing films were more stretchable. Lipid addition did not induce a notable decreased in water vapour permeability of the films, but oxygen permeability highly increased when they contained oleic acid. All films were highly transparent, with very small differences among formulations, although their gloss values increased when lipids were added. The incorporation of α-tocopherol greatly increased the antioxidant capacity of the films which affected oxygen permeability.     

The effect of high hydrostatic pressure on the flow behaviour of skim milk–gelatin mixtures

The flow behaviour of aqueous solutions of gelatin, and skim milk–gelatin mixtures treated by high-pressure processing (HPP) were investigated. HPP was carried out at 5 °C for 15 min, at 150 MPa, 300 MPa, 450 MPa and 600 MPa, and the gelatin concentrations were varied from 0 to 1 wt.%. Viscosity measurements showed that the HPP treatment did not affect the flow behaviour of gelatin alone, nor that of the skim milk–gelatin mixtures made with < 0.4 wt.% gelatin. However, at gelatin concentration > 0.4 wt.%, the mixtures treated with 300 and 450 MPa exhibited a peculiar flow behaviour, where at intermediate shear rates the viscosity was higher than that of the non-treated mixture or the mixtures treated at 150 MPa and 600 MPa. Particle size measurements showed that for gelled mixtures (> 0.4 wt.% gelatin) 300 MPa HPP treatment resulted in an increase in the particle size, while at all other pressure treatments (> 150 MPa), a shift in particle size distribution to lower sizes was observed. Confocal microscopy showed that these skim milk–gelatin mixtures were phase-separated with a gelatin continuous phase, this was confirmed by dynamic rheological measurements which showed that qualitatively the viscoelastic properties of the mixtures were the same. A mechanism of the effect of high-pressure treatment on the casein micelle in skim milk–gelatin mixtures is proposed.Industrial relevanceThis fundamental work, dealing with the effect of high pressure on the physicochemical properties skim milk–gelatin mixtures could be relevant to the industry in several ways. Firstly, skim milk–gelatin mixtures are widely used in the dairy industry, particularly in yoghurt manufacture, where gelatine is used as a stabiliser. In addition the application of High Hydrostatic Pressure to such a system is also relevant, as this technology could be used as a substitute to the conventional heat treatment processes. Secondly, an important finding of this study is that under certain conditions of high pressure and gelatine concentration, an increase in viscosity is observed at intermediate shear-rate (between 10 and 100 s^?1). This is highly relevant to Industry if the system requires subsequent pumping. Thirdly, from a sensory view point, this range of shear rates (10 and 100 s^?1) is comparable to that experienced by a food bolus during swallowing. Thus, this effect of high pressure on the viscosity can influence sensory attribute of the skim milk–gelatin food system.     

Effect of the incorporation of antioxidants on physicochemical and antioxidant properties of wheat starch–chitosan films

Blend edible films were prepared from wheat starch (WS) and chitosan (CH) with glycerol as plasticizer. Four active ingredients (antioxidants) were added, namely basil essential oil, thyme essential oil, citric acid and α-tocopherol. The starch:antioxidant mass ratio was 1:0.1. Prior to characterisation, the films were conditioned at 25 °C–53%RH as to their structural, mechanical, optical and barrier properties. The antioxidant capacity of the active ingredients was determined by means of a spectrophotometric method. The incorporation of antioxidants led to a heterogeneous film microstructure, mainly in those containing α-tocopherol, which affected the surface roughness. Yellowness was induced in films when α-tocopherol was added and no notable colour changes were observed in the other cases, although all the antioxidants increased the transparency of the films. Despite of the fact that the mechanical properties were barely affected by the incorporation of antioxidants, citric acid promoted an increase in the elastic modulus but a decrease in film stretchability. The water vapour barrier properties of the films were only slightly improved when citric acid and α-tocopherol were added, whereas the oxygen barrier properties were significantly improved in all cases. The greatest antioxidant capacity of the films was reported for films containing α-tocopherol, which exhibited the highest antioxidant power.     

The effect of freeze–thaw cycles on microstructure and physicochemical properties of four starch gels

The effect of repeated freeze–thaw (FT) cycles (up to seven) on microstructure, thermal and textural properties of four starch gels from various botanical origins (gingko, Chinese water chestnut, potato and rice) was investigated and compared by scanning electronic microscope, differential scanning calorimetry and texture analyzer. The chemical composition and molecular structure of four starches were also examined. The Chinese water chestnut, potato and rice starch gels formed a honey-comb structure after 7 FT cycles, while gingko starch gel exhibited lamellar structure. The 7 FT cycles decreased the transition temperatures and enthalpies of four starches in comparison with each native starch, and the retrogradation percentage followed the order: rice > gingko > Chinese water chestnut > potato. The 7 FT cycles increased the hardness of all the evaluated starch gels and decreased springiness and cohesiveness. Results showed that the molecular structure of starches caused notable differences to the microstructure and textural properties of starch gels. The higher amount of longer branch chain (degree of polymerization (DP) > 18) might benefit the formation of the lamellar structure of gingko starch. The percentage of branch chains (DP 18–23) was negatively related with the springiness and cohesiveness of native starch gels, while the percentage of medium chains (DP 12–17) was positively related to the springiness of starch gels after 7 FT cycles.     

Tribocharging properties of wheat bran fragments in air–solid pipe flow

Triboelectric separation (TS) has been used to separate aleurone particles from wheat bran fragments, but its mechanism remains poorly understood. In this study, the tribocharging properties of different bran tissues in the pipes made of Teflon, Nylon and stainless steel were investigated. The effects of air flow rate and water content on tribocharging were also studied. The results showed that, after tribocharging with Teflon pipe, the total charges of the bran fragments were positive, and decreased with the times of tribocharging, while, in Nylon pipe, the total charges obtained by the bran fragments were negative initially, then increased to be positive. The more aleurone cells in bran fragments, the more their total charges changed. After tribocharging with steel pipe, the total charges of bran fragments were positive and almost constant. The results of TS indicated that the polarities of the charges obtained by aleurone and pericarp particles were reversed by the pipe materials. Based on the results, a mechanism of tribocharging in air–solid pipe flow was built to explain the charging diversity of the wheat bran tissues in TS.     

Effect of high pressure processing on rheological and structural properties of milk–gelatin mixtures

There is an increasing demand to tailor the functional properties of mixed biopolymer systems that find application in dairy food products. The effect of static high pressure processing (HPP), up to 600 MPa for 15 min at room temperature, on milk–gelatin mixtures with different solid concentrations (5%, 10%, 15% and 20% w/w milk solid and 0.6% w/w gelatin) was investigated. The viscosity remarkably increased in mixtures prepared with high milk solid concentration (15% and 20% w/w) following HPP at 300 MPa, whereas HPP at 600 MPa caused a decline in viscosity. This was due to ruptured aggregates and phase separation as confirmed by confocal laser scanning microscopy. Molecular bonding of the milk–gelatin mixtures due to HPP was shown by Fourier-transform infrared spectra, particularly within the regions of 1610–1690 and 1480–1575 cm⁻¹, which reflect the vibrational bands of amide I and amide II, respectively.     

Mechanical properties of κ-carrageenan in high concentration of sugar solutions

While the mechanism of gelation of carrageenan in an aqueous environment, via a coil–helix transition followed by aggregation, is well accepted, its behaviour in highly concentrated sugar is still not well understood. Therefore, the effect of biopolymer and salt concentration on the gelling properties of κ-carrageenans in the presence of high concentrations of sugars was investigated rheologically. A solution of 1% κ-carrageenan in the presence of 10 mM KCl and 87.5% corn syrup did not form a measurable network whereas 1% κ-carrageenan in the presence of 10 mM KCl in aqueous solution forms a gel. Gelation was again observed as KCl concentration was increased to 40 mM KCl. An increase of κ-carrageenan concentration from 1 to 2% with 10 mM KCl present did not restore the capacity for gelation. The effect of type of the sugar solution was also investigated by substituting a corn syrup/glucose syrup mixture for the original corn syrup. In the presence of corn syrup/glucose syrup mixture and salt at concentrations higher than 40 mM KCl, a different gelation behaviour was observed: a gel structure was already present at high temperature and a glass transition was measurable at the lowest temperatures. We believe this study gives new insights into the molecular state of carrageenan in the presence of high concentrations of sugars.     

Influence of sodium chloride on shear flow induced starch–gluten separation from Soissons wheat dough

Wheat dough can be separated into a starch-rich and a gluten-rich fraction by subjecting the dough to curvilinear shear flow. This paper presents the effect of salt (NaCl) addition on the shear-induced separation process. The separation (defined as the changes in protein concentration in the various layers, compared to the starting material) was promoted by NaCl addition up to a concentration of 4 w%. Dough without NaCl showed limited separation, but this effect could be partly compensated by a decreased processing time. Rheology measurements did not show clear differences in G′ and tan δ value, for dough with different NaCl concentration. But, shear stress and normal force did vary for various NaCl concentrations when applying a constant shear rate.     

Gel mechanical properties of milk whey protein–dextran conjugates obtained by Maillard reaction

The effect of Maillard reaction on the mechanical properties of whey protein isolate (WPI) heat-induced gels was evaluated. WPI and dextran (15–25 kDa) conjugates were obtained by controlled dry heating during storage at 60 °C and 63% relative humidity for 2, 5 and 9 days. Changes in browning intensity and content of free amino groups were used to estimate the Maillard reaction. A decrease in free amino groups of WPI was observed when increasing polysaccharide concentration and reaction time. An increase in both a* and b* CIE Lab colour parameters indicated the development of a reddish-brown colour, typical of the Maillard reaction. Uniaxial compression and stress relaxation tests were performed to measure the mechanical properties of mixed and conjugate gels. Maillard reaction significantly modified the mechanical properties of WPI/DX gels, and even prevented fracture when conjugate gels were subjected to 80% deformation in uniaxial compression test.     

Solutions properties and solute–solvent interactions in ternary sugar–salt–water solutions

Viscometric constants were used to provide information on solute–solvent interactions in ternary water–sugar–salt solutions. Comparison was made between pure water and aqueous salt solution as solvents affecting the behaviour of small carbohydrates. The determination of intrinsic viscosity was made more accurate by applying triple extrapolation of the three equations (Huggins, Kramer and Meffroy-Biget). Results obtained with this triple extrapolation method were compared to that obtained with the Jones–Dole equation usually used. The B coefficient of the Jones–Dole equation was interpreted in terms of its components (B_size) and (B_structure), respectively assigned to the hydrodynamic volume and the contribution to solvent structural change. The determination of the apparent molar volumes in pure water enabled calculation of the hydration numbers. The determined apparent molar volumes of the studied sugars in aqueous salt solutions suggested a dehydration of the sugars explained by sugar–salt interactions. The most important perturbations observed in LiCl solutions compared to those in NaCl solutions were explained by LiCl being surrounded with more water molecules.     

Effect of heating–cooling on rheological properties of tapioca starch paste with and without xanthan gum

The effect of xanthan gum (Xan) on pasting and gelatinization behavior of tapioca starch (TS) was investigated. Rheological measurements of TS/Xan mixtures with 5% w/w total polysaccharide concentration at different mixing ratios (10/0, 9.5/0.5, 9/1 and 8.5/1.5) were performed to understand the pasting and gelatinization behavior of TS with and without Xan on heating–cooling cycle using a Rapid Visco Analyzer (RVA) and conventional rheometers. Xan increased storage modulus (G′) and loss modulus (G″) of TS dispersions during gelatinization process. Pastes of TS/Xan tended to be more solid-like, i.e., G′ larger than G″, with increasing Xan. The G′ of TS/Xan paste increased when kept at 10 °C indicating the network formation. Pasting temperatures, peak viscosity, final viscosity and breakdown values of TS increased with increasing Xan content but the opposite result was observed in setback value from RVA measurement. Temperature dependence of steady shear viscosity became less pronounced with increasing Xan content on both cooling and reheating indicating that Xan made the mixture more thermally stable. All the results suggest that the sample preparation and measuring conditions influence the rheological properties of TS/Xan mixtures, which should be taken into account in food application.     

Rheological and textural studies of fresh and freeze-thawed native sago starch–sugar gels. II. Comparisons with other starch sources and reheating effects

The viscoelastic and textural properties of freshly prepared and freeze-thawed sago starch–sugar gels were studied in comparison with other native starches from corn, wheat, tapioca, and potato. The gelatinisation and retrogradation properties of starches were studied using a DSC while the pasting properties of starch–sugar mixtures during the cooking period were studied using a starch pasting cell. The freeze-thaw stability of gels was evaluated by gravimetric measurements of the water of syneresis. The different starches gave properties which varied following to their botanical sources. High-amylose cereal starches (wheat and corn) produced harder gels, while low-amylose root starch (tapioca) produced softer gels. Sago and potato gels showed close similarities in their viscoelastic and textural characteristics. Although the freeze-thaw cycle greatly increased the viscoelasticity and hardness of these two gels, reheating at high temperature significantly reduced these negative effects and resulted in partial recovery of the gel structures. Sago starch produced gels with very low syneresis and high cohesiveness, implying its potential use as a gelling agent in the frozen food industries.     

Characteristics of a calcium–milk coagulum

The texture, microstructure and composition of a milk coagulum obtained by coagulating milk with calcium chloride and heat were evaluated. A direct relationship was established between the microstructure and texture of the calcium–milk coagulum. The microstructure was comprised of casein micelles that were interlinked by appendages or fused with each other depending on the nature of the pre-heat treatment employed. The casein micellar network also entrapped fat globules. The pre-heat treatment of milk and the pH of milk during coagulation affected the hardness, adhesiveness, protein content and microstructure of the calcium–milk coagulum significantly. This study characterises a calcium–milk coagulum as a novel dairy product which differs from an acid coagulum in texture, microstructure and composition.     

Effects of fatty acid chain length on properties of potato starch–fatty acid complexes under partially gelatinization

A series of starch–fatty acid samples were prepared using potato starch and four fatty acids differing in their chain length, including lauric (C12), myristic (C14), palmitic (C16), and stearic (C18) acids. The results indicated that the fatty-acid chain length played a significant role in altering the properties of potato starch–fatty acid complexes. The complexing index of potato starch–fatty acid complexes decreased from 0.38 to 0.18 with increasing carbon-chain length. V-type crystalline polymorphs were formed between starch and four fatty acids, with shorter chain fatty acids preserving more crystalline structure. X-ray diffraction studies revealed that the degree of crystallinity exhibited by the starch samples was dependent on the fatty-acid chain length. In the Fourier transformed infrared spectrum of the samples, the new spikes at 2917, 2850, 1018, and 720 cm^?1 were assumed to be related to the presence of fatty long chains. The formation of amylose–fatty acid complex inhibited granule swelling of potato starch, w\ith longer chain fatty acids showing greater inhibition. Scanning electron microscopy microscopic examination indicated that amylose–fatty acid interactions taken place during starch gelatinization retarded the destruction of the granules.     

Genetic polymorphism of ovine milk proteins: its influence on technological properties of milk — a review

Current knowledge of the genetic polymorphism in ovine milk proteins including heterogeneity detected and their relationships with the technological properties of milk is reviewed. In the casein fraction a great heterogeneity has been determined either by the presence of genetic variants or other factors such as a discrete phosphorylation level and the coexistence of protein forms of different chain length. In the whey fractions, three genetic variants (A, B, and C) are described for β-lactoglobulin (β-LG), and two for α-lactalbumin (α-LA). The topics discussed include the rennetability of ovine milk, cheese yield and susceptibility of β-LG genetic variants to heat denaturation as well as the findings concerning the relationships between ovine milk protein polymorphism and milk production and composition. However, further investigation is needed in order to better outline the relevant features of polymorphism and technological properties of ovine milk.     

Effect of acid concentration and treatment time on acid–alcohol modified jackfruit seed starch properties

The properties of starch extracted from jackfruit (Artocarpus heterophyllus Lam.) seeds, collected from west Assam after acid–alcohol modification by short term treatment (ST) for 15–30 min with concentrated hydrochloric acid and long term treatment (LT) for 1–15 days with 1 M hydrochloric acid, were investigated. Granule density, freeze thaw stability, solubility and light transmittance of the treated starches increased. A maximum decrease in the degree of polymerisation occurred in ST of 30 min (2607.6). Jackfruit starch had 27.1 ± 0.04% amylose content (db), which in ST initially decreased and then increased with the severity of treatment; in LT the effect was irregular. The pasting profile and granule morphology of the treated samples were severely modified. Native starch had the A-type crystalline pattern and crystalline structure increased on treatment. FTIR spectra revealed slight changes in bond stretching and bending. Colour measurement indicated that whiteness increased on treatment. Acid modified jackfruit seed starch can have applications in the food industry.     

Thermal,mechanical and water adsorption properties of corn starch–carboxymethylcellulose/methylcellulose biodegradable films

The objective of this study was to investigate the effect of the addition of methylcellulose and carboxymethylcellulose on the thermal, mechanical and water adsorption properties of starch-based films plasticized with glycerol or polyethylene glycol (PEG). Mechanical tests showed that as the methylcellulose and carboxymethylcellulose proportion increased, starch films became more resistant to break, resulting in higher TS values. Besides there has been a positive effect on the elasticity of starch films realized by a considerable increase in E% values. Depending on the plasticizer type, either single or dual glass transitions were seen in DSC thermograms. One glass transition temperature was observed for films plasticized with glycerol, on the contrary, dual glass transitions were detected for PEG plasticized films. This behavior was attributed to the phase separation of the PEG. In addition, the presence of an endothermic peak in the thermograms of PEG plasticized films was taken as another indicator of the phase separation. As a result, it was suggested that PEG was not as compatible as glycerol with the composite polysaccharide matrix and plasticizer type was the main factor that shaped the thermal profiles of the film samples. Water adsorption isotherm data showed that samples displayed nonlinear sorption profile which is typical for hydrophilic films. In all films tested, equilibrium moisture contents, increased almost linearly up to a a_w of 0.65–0.85, beyond where a sharp increase was noted. Adsorption data was adequately fitted by BET and GAB models. Eventually, it can be concluded that film forming properties of starch can be improved by incorporation of methylcellulose and carboxymethylcellulose to the polymer matrix.